Field of the Invention
The present invention relates to an element substrate, a printhead, and a printing apparatus and, particularly to, a full-line printhead that prints according to, for example, an inkjet method, and a printing apparatus that performs printing using the same.
Description of the Related Art
There is conventionally known an inkjet printhead that discharges ink from a plurality of orifices using thermal energy. To obtain stable discharge characteristics in this printhead, it is necessary to apply a stable voltage to heaters. A plurality of heater arrays are arranged on an element substrate for a printhead. When all heaters of one heater array are concurrently driven, large currents flow to ground wirings and driving power wirings that supply power to the heaters, and the voltage considerably drops due to the wiring resistance. To reduce the voltage drop, the number of heaters to be concurrently driven is limited in recent element substrates for a printhead. More specifically, the plurality of heaters are divided into a predetermined number of blocks and sequentially driven, that is, so-called time-divisional driving is performed, thereby implementing stable voltage application to the heaters.
When a plurality of heaters are concurrently driven, large currents flow to driving power wirings and ground wirings. At the leading and trailing edges of the large current supply, electromagnetic noise is generated by inductive coupling in the driving power wirings and the ground wirings.
The driving power wirings that apply a driving voltage to the heaters on the element substrate, the ground wirings, logic signal wirings that send signals to logic circuits on the element substrate, and the like are parallelly arranged on the printhead. Hence, the electromagnetic noise generated by the above-described inductive coupling may be superimposed on a logic signal and cause an operation error in a logic circuit provided on the element substrate. To prevent this, the element substrate that performs time-divisional driving executes control to delay the timing of a driving pulse to be applied to each heater in a selected block in nanoseconds. A current flowing in unit time is made small in this way, thereby suppressing occurrence of electromagnetic noise and preventing operation errors in the logic circuits on the element substrate (see Japanese Patent No. 3323597 and Japanese Patent Laid-Open No. 2008-114378).
To implement quicker printing, there has recently been proposed a full-line printhead that has a print width equal to or more than the width of a printing medium in advance by arranging a plurality of element substrates. The full-line printhead can perform high-speed printing because it is theoretically unnecessary to scan and move the printhead, and is used in a printing apparatus for business or industrial use.
Since the print width of the full-line printhead is long, the wiring length of a driving power wiring from the power supply circuit or capacitor to the element substrate and the wiring length of a ground wiring also become long. When the wiring lengths are long, the parasitic inductance components of the wirings are large. For this reason, when a large current flows, ringing occurs, and the driving voltage of the heaters largely varies. When the timing of a driving pulse to be applied to each heater in a selected block is delayed in a state in which the driving voltage of the heaters is ringing, a waveform difference occurs between the driving pulses to be applied to the heaters, and a difference between energies generated by the heaters is generated. This energy difference causes a difference between the amounts of ink discharged from the orifices, resulting in density unevenness in a printed image.